Apparatus for opening cans and sharpening knives



Sept. 1, 1964 A A. L. A. POSENER 3,146,555

APPARATUS FOR OPENING CANS AND SHARPENING KNIVES Original Filed March 5, 1962 4 Sheets-Sheet 1 w I U $2 if, FM 74.

w 1' 55/ firm/9w z. 2%

Sept. 1, 1964 A. L. A. POSENER 3,146,555

APPARATUS FOR OPENING CANS AND SHARPENING KNIVES Original Filed March 5, 1962 4 Sheets-Sheet 2 INV EN TOR. 424mm 4 A. flafa/m Sept. 1, 1964 A. 1.. A. POSENER 3,146,555

APPARATUS FOR OPENING CANS AND SHARPENING KNIVES 4 Sheets-Sheet 3 Original Filed March 5, 1962 Y/Y/ ///f Se t. 1, 1964 A. L. A. POSENER APPARATUS FOR OPENING CANS AND SHARPENING KNIVES 4 Sheets-Sheet 4 Original Filed March 5, 1962 United States Patent 3,146,555 APPARATUS FOR OPENING CANS AND SHARPENING KNIVES Armand L. A. Posener, La Habra, Califi, assignor to Udrco Electric (30., Los Angeles, Calif, a corporation f Ca ifornia Orig nal application Mar. 5, 1962, Ser. No. 177,620. Divided and this application Feb. 7, 1963, Ser. No. 256363 3 Claims. (Cl. 51-128) This is a divisional application of the co-pending patent application, Serial No. 177,620, filed March 5, 1962, and is directed to improvements in apparatus for automatically opening cans and sharpening knives.

It is a general object of the apparatus for performing the combined operation of opening cans and sharpening knives to have an optimum utility in the home kitchen at a minimum of expense to the consumer. To accomplish this it is desired that the apparatus be simple, compact and portable as Well as rugged in its deisgn. Further, the apparatus should operate automatically to simply and efficiently open cans and sharpen knives with a minimum or servicing over a maximum period of time.

To provide this, can opener-knife sharpener apparatus generally includes, varying with specific designs, the basic combination of an electric motor mounted within a housing to rotate both a grinding wheel and a driving wheel. The driving wheel is rotatably carried by the housing to engage the under side of the bead of a can. Movably coupled to the housing, above the driving wheel, is a rotary cutter. The cutter is shiftable, by operation of a hand-operated lever, into cutting position with the driving wheel by engaging the top of the can immediately adjacent the head. In this position rotation of the driving wheel rotates the can in contact with the rotary cutter to completely sever the top from the can.

Although by this combination of elements the prior art apparatus has effected a can opening and knife sharpening operation, they have only partially accomplished the above objective. For example, to energize the electric motor, thereby causing a rotation of the driving wheel as well as the grinding wheel, a switch is provided which is generally operated by the final movement of the hand-operated lever in shifting the rotary cutter into cutting position with the driving wheel. Thus, to open a can or to perform a grinding operation with the prior art apparatus, the operator must often manually maintain the lever in a position to close the switch. When sharpening a knife this means that only one hand is free to hold and guide the knife, a fact which may lead to nonuniform sharpening of the blade unless special guiding apparatus is provided. When employing the apparatus to open a can, this means that the operator is required to remain at the apparatus until the can is completely open. He is not free to perform other acts.

Further, it has been found in practice that the rotary cutter of most prior art apparatus, with use, tends to become frozen by foreign matter working between the rotary cutter and the coupling to the housing. When this occurs the cutting operation is materially impeded. Freezing of the cutter in such apparatus is prevented by frequently cleaning the cutter and its coupling to the housing. This entails completely removing the cutter from the housing.

In addition, the driving wheel design of the prior art apparatus is such that the wheel, in contacting the underside of the bead, also engages the side of the can below the bead. Thus, as the can rotates, the driving wheel tends to crush and tear any paper label on the can. The torn label accummulates at the driving wheel to interfere with the rotary movement of the can which impedes the cutting operation of the can opener.

Also, when utilizing a motor driven grinding wheel to sharpen knives, it is desirable to provide means for preventing damage to the knife blade resulting from abnormal pressure of the blade on the wheel. This may be accomplished by effectively stopping the grinding wheel when the blade pressure on the wheel reaches a predetermined safe maximum. In the past this has been accomplished by employing a special motor design and by maintaining a particular relationship between the motor speed power requirement and the diameter of the grinding wheel, which combination stalls the motor when the predetermined safe blade pressure is reached. Such an arrangement, however, is both complex in design and relatively expensive. Another prior art arrangement for protecting the grinding wheel employs a pair of critically designed spring-loaded clutches to provide a slipping coupling between the grinding wheel and the motor drive shaft, see e.g. Bednarski Patent 2,898,709. Such a dual clutch arrangement, however, has also proven to be unduly complex in design and relatively expensive to construct.

The present invention, therefore, provides an improved can opener and knife sharpener design which is fully automatic, simple and eificient in its operation and one which overcomes the above-identified weaknesses in the prior art apparatus.

To accomplish this, the present invention combines a housing having an electric motor mounted therein, a shaft coupled to the motor, a freely rotatable grinding wheel mounted on the shaft and coupled thereto, and a driving wheel rotatably coupled to the shaft. The shaft and the grinding wheel are rotatably locked together by singular means. The locking means, which preferably takes the form of a slipping clutch, has a predetermined torque transfer characteristic which provides slippage between the shaft and the grinding wheel when excessive pressures are exerted against either side of the grinding wheel by a blade.

The driving wheel is carried by the housing and is positioned to contact the underside of a can bead to rotate the can in response to rotary movement of the shaft. The driving wheel has an annular toothed portion which engages the under side of the bead and means for limiting the contact of the toothed portion with the side of the can below the bead. Preferably, the limiting means takes the form of an annular shoulder extending radially outward beyond the toothed wheel. The shoulder engages the side of the bead when the toothed portion is in contact with the under side of the bead to maintain the toothed portion out of contact with the side of the can.

Movably supported by the housing above the driving wheel is a rotary cutter. The rotary cutter is adapted for shifting movement into cutting position relative to the driving wheel by engaging the top of the can immediately adjacent to the bead. Preferably, the rotary cutter is hearing mounted for rotation relative to the housing by a sleeve arrangement composed of a plastic-like material. The sleeve arrangement prevents the rotary cutter from freezing. A clean cutting operation by the rotary cutter is thus assured.

The rotary cutter is shifted into cutting position relative to the driving wheel by hand-operated means. Once the cutter and driving wheel are in cutting position, the handoperated means is engaged by a lock member which maintains it in position. Moreover, the hand-operated means is adapted to energize the motor automatically after the rotary cutter is in cutting position relative to the driving wheel.

Means are further included for automatically shutting a 9.) off the motor when the top has been completely severed from the can. As a consequence, after once energizing the electric motor, the operator is free.

In view of the above, the present invention, by its specific combination of improved design features, provides overall improved apparatus for automatically opening cans and sharpening knives that eliminates the need for continuous manual control while in operation and provides an improved rotary cutter-drive Wheel combination which does not freeze with use and which does not bind or tear the paper labels of the can to impede the cutter operation; and coupling the grinding wheel to the motor shaft to provide an efficient yet inexpensive coupling between the shaft and the wheel that prevents damage to knife blades during the sharpening operation.

The above, as well as other features of the present invention, may be more clearly understood by reference to the following detailed description when considered with reference to the drawings, in which:

FIGURE 1 is a front view of the apparatus of the present invention;

FIGURE 2 is a sectional right side view of the apparatus of the present invention taken along line 2-2 of FIGURE 1;

FIGURE 3 is a partial rear view of the apparatus with certain parts broken away to illustrate the novel automatic shut-oif feature;

FIGURE 3A is a schematic diagram of the electrical circuit of the present invention;

FIGURE 4 is a sectional view of the apparatus taken along line M of FIGURE 1;

FIGURE 5 is a sectional view taken along line 44 of FIG. .1 with a can engaging the driving wheel of the apparatus;

FIGURE 6 is a cross section view of the grinding wheel and clutch coupling arrangement taken along line 66 of FIGURE 2;

FIGURE 7 is a partial section taken along line 77 of FIG. 1 to more clearly illustrate the locking arrangement for the hand-operated lever of the exemplary embodiment of the invention; and

FIGURE 8 is a partial side view of the apparatus with certain parts broken away to illustrate an alternative arrangement of the electric motor grinding wheel and cooling fan part of the present invention.

Although the specific improvements embodied by the overall design of the present invention are applicable to power can openers and knife sharpeners in general, they will be described in detail as specific improvements in an electric can opener and knife sharpener apparatus of the type descibed in the US. Patent 2,897,589, issued August 4, 1959. Accordingly, for more specific details on the operation of the apparatus not constituting parts of the present invention, reference may be made to this patent.

Referring to the drawings, particularly FIGS. 1 and 2, the exemplary embodiment of the present invention includes a housing represented generally at 10, which includes three body sections, namely, a front section 12 having a vertical side or front wall 14, a rear section 16 coupled to the front section by a screw member 1%, and a cover section 20 mounted on the rear section 16 to cover a knife sharpening portion of the apparatus indicated generally at 151.

Mounted within the housing by an arm member 22 which extends from the side wall 14 is an electric motor 24. Coupled to the electric motor for rotation therewith is a shaft 26, which extends on either side of the motor 24.

The end of the shaft 26 adjacent the side wall 14 forms a gear 28. The gear 28 engages a gear 29 in a reduction gearing arrangement, represented generally at 3t). The gear 29 is staked to pinion 30 which engages gear 32. Gear 32 is aflixed to shaft member 34 which is journalled in the side wall 14 for rotation about the centerline axis of gear 32. Extending around the shaft 34- and supported within a tubular opening 36 in the side wall 14 is the hub or hollow shaft 38 of a driving wheel 40. The driving wheel 40 abuts an outer surface of the side wall 14 adjacent the tubular opening 36 and is coupled to the shaft 34 by a screw 42. In this manner, the driving Wheel 40 rotates with the gear 32 in response to the rotation of the motor shaft as.

The driving wheel 46 includes an annular toothed portion 44 adapted to contact the under side of the bead 46 of a can 48 (illustrated in FIGS. 4 and 5). Immediately adjacent the gear or toothed portion 44 is an annular shoulder 50. The annular shoulder 50 extends radially outward beyond the toothed portion 44 between the toothed portion and the side wall 14. The toothed portion 44 is proportioned to allow the annular shoulder 50 to act as a stop for the can 48. Specifically, the shoulder 50 engages can bead 46 to prevent the outer surface of the toothed portion 44 from contacting the side of the can 48. This prevents the driving wheel 40 from damaging a paper label that might be on the can 48; and it avoids. the possibility of a torn label binding the driving wheel 40.

Positioned along the side wall 14 and apertured at 70 to allow the driving wheel 40 to extend therethrough is a mounting plate 52. The mounting plate 52 is movably coupled to the side wall 14 by a a pair of screw members 54 and 56. As illustrated in FIGURE 1 and described in detail in the aforementioned US. patent, the screw member 54 extends through an opening 58 in the mounting plate 52 and is coupled to a cylindrical hub 60. The hub 6% forms a component part of a hand-operated lever arm 62 and is mounted for rotation in an opening 64 in the side wall 14. The screw 56 is threaded into Wall 14 through a longitudinal slot 66 in the mounting plate 52. Due to this arrangement, movement of an end 68 of the lever arm 62 in a clockwise direction (with reference to FIG. 1) produces an upward sliding movement of the mounting plate 52 relative to the side vertical wall 14.

Extending outwardly (toward the front of the apparatus) from the lower part of the mounting plate 52 is a shoulder member 72. The shoulder member 72, as illustrated in FIGURE 5, is engaged by the side of the can 48 when it is positioned for opening. The shoulder 72 posi tions the can laterally from the outer face of the driving wheel 40. It also acts as a guide for the can as it rotates in response to the rotary movement of the driving wheel 40.

Extending outward and down from the mounting plate 52, at a point above the driving wheel 40, is a support member or projection 74. A cutter 78 is rotatably supported on the support member 74 by a screw 76. The rotary cutter 78 is positioned so that its annular cutting edge 80 can be moved immediately adjacent the outer surface of the driving wheel 40. Further downward movement of the rotary cutter 78 causes cutting edge 80 to puncture the top of the can 48 directly adjacent the inner side of the head 46. At this point it cooperates with the driving wheel 40 and the guide shoulder 72 to clamp the can 48 in a cutting position with the under side of the head 46 bearing on the toothed portion of the driving wheel 40. Rotary movement of the driving wheel 43 thereafter rotates the can 48 because the teeth of gear 44 grip head 46. The result is that the cutting edge 80 severs the top from the can 48 adjacent the inner side of the bead 46.

As illustrated in FIGURE 2, a sleeve member 82 supported on screw 76 acts as a bearing for the rotary cutter 78. Preferably, the bearing member 82 is formed of a plastic-like material such as nylon or Teflon. This provides a long life bearing for the rotary cutter 78 and it substantially prevents the cutter from freezing due to impaction of foreign matter between the cutter 78 and its support member 74.

Also coupled to the mounting plate 52, at one side of the rotary cutter 73, is a spring-loaded arm 84 carrying a magnet 86. The arm 84 is normally maintained in a horizontal plane outward from the mounting plate 52 to provide close spacing between the top of the can 48 and the magnet 86 when the can 48 is positioned for opening, as illustrated in FIGURE 4. In this manner, the magnet 86 readily attracts the top of the can 48 and the spring biased arm 84 moves downwardly, as indicated in FIGURE 5, to allow the top to engage the magnet. After the top of the can 48 is completely severed from the can, the spring returns the arm 84 (and the top of the can) to its normal position.

To selectively energize the electric motor 24 to produce the above-described rotary movement of the driving wheel 40, the present invention utilizes a mechanically operated switch 88. The switch, which is most clearly represented in FIGURE 3, operates in an electrical circuit illustrated in FIGURE 3A. In particular, the switch arrangement includes a normally open switch 88 connected between one side of the winding of motor 24 and an electrical power plug 99. The plug 98 is connectible to a conventional 120 volt 60 cycle A.C. power supply. To provide for the selective closing of the switch 88, an arm member 92 is coupled to the movable switch arm 94 of the switch 88. The arm member 92, which includes a vertical slot 96, extends upward from the switch 88 and through an opening 98 in the top of the front section 12 of the housing 16 (FIG. 3). Extending from the rear of the wall 14 through the slot 96 is a lug 180. The slot 96 is longer than the lug 180 to allow the arm 92 to be movable in a vertical direction, guided by the lug 180. Extending around the arm 92, between a shoulder 192 and the upper mounting surface of the switch 88, is a spring member 104. The spring member 164 normally urges the arm 92 upward to extend beyond the opening 96. In this position the switch 38 is open to prevent current flow to the motor 24. Since the arm member 92 normally extends above the top of the housing the lever arm 62 in shifting the rotary cutter 78 into cutting position with the driving wheel 40 engages the arm 92. Downward movement of the lever arm 62 thus causes the arm 92 to mechanically close the switch 88, thereby completing an electrical circuit to energize the motor 24.

When the lever arm 62 is in a position to effect an energizing of the motor 24, it is engaged by locking arrangement that holds the arm in a down position and thereby maintains the switch 88 closed. This permits the operator, after once energizing the motor, to move away from the apparatus of the present invention and perform other acts within the kitchen. Preferably, the locking apparatus of the present invention includes, as illustrated in FIG- URE 6, a locking pin 106 extending from the lower surface of the lever arm 62. The locking pin 106 has an enlarged, diamond-shaped end section 198 which passes through an opening 110 in the top of the front section 12 of the housing 18. In passing through the opening 110 the pin 106 engages and is forced within the central opening 112 of a retaining spring 114. The retaining spring 114 is positioned within the slot 116 formed by cooperating adjacent surfaces of the top of the front section 12 and a plate 118.

To further provide complete automatic operation of the can opener apparatus of the present invention, means are included for automatically shutting off the motor 24 after the top has been completely severed from the can 48. Preferably, the automatic shut-off arrangement of the present invention, as illustrated in FIGS. 3-5, includes a normally closed switch 126. The switch 126 is electrically connected between the motor 24 and the plug 90, thereby permitting the completion of an electrical circuit for the motor 24 when switch 88 is operated.

The switch 120 as schematically illustrated, includes apair of fixed electrical contacts 122 and 124 spaced above and below a movable switch arm 126. The switch arm 126 normally engages the contact 124 when a can is not in the opener (illustrated in FIG. 4). When a can is laced in position, arm 126 engages contact 122 (switch 120 closed) and when the top has been completely severed from the can 48, arm 126 is intermediate contacts 122 and 124 which opens the electrical circuit including the motor 24 thereby causing the motor to shut off.

Switch must be held closed when a can is not inserted in the opener so that the motor may be energized to perform other operations of the apparatus. For example, as disclosed in the drawings, the apparatus includes a knife sharpener indicated generally at 151. It must specifically be operable when a can is not being opened.

To effect the automatic opening of the switch 120, the switching apparatus of the present invention includes an arm member 128 extending through the mounting structure of the switch 120. The arm member 128 is coupled to the switch arm 126 within the mounting structure and includes an enlarged portion 130 which extends upward along the rear of the side wall 14. The enlarged section 130 has a vertical slot 132 formed therein. Extending from the wall 14 through the slot 132 is a lug member 134 having an annular slot 136 therein. Positioned around the lug 134 and disposed within the slot 136 is a snap ring 138. The snap ring 138 extends radially beyond the lug 134 to engage the sides of the enlarged portion 139 adjacent the slot 132. In this manner the combination of the lug 134 and the snap ring 138 provides a vertical guide for the arm member 128.

As illustrated, the arm member 128 extends downward through the mounting structure of the switch 128. Positioned around the arm 128 between a shoulder 14% and the lower surface of the mounting structure for the switch 128 is a spring 142. The spring 142 normally exerts a downward forces on the shoulder 148 to urge the arm 128 in a position to keep the switch 120 closed (with the switch arm 126 engaging the contact 124).

Coupled to the enlarged section 130 to extend horizontally outward through aperture 145 in wall 14 and an opening 144 in the mounting plate 52 is a can guiding arm 146. Due to the spring 142 the can guiding arm 146 is effectively spring-loaded and is normally positioned (absent a can) along the mounting plate 52 at the upper edge of the driving wheel 40, as illustrated in FIGURES 1 and 4. In positioning the can 48 in cutting position, with the ead 46 resting on the toothed portion of the driving wheel, the can guiding arm 146 is raised to engage and rest upon the top of the can 48, as illustrated in FIGURE 5. This is accomplished by moving the lever arm 62 away from the top of the housing 10 to move the rotary cutter 78 upward from the driving wheel 41). This causes the lower edge of the opening 144 in mounting plate 52 to lift the can guiding arm 146 and the arm member 128. The movement of the arm member 128 produces a movement of the switch arm 126 (mounted in switch 120 and shown schematically in FIG. 3A. Downward movement of the lever arm 62 then allows the spring biased can guiding arm 146 to engage the top of the can 48 as illustrated in FIG. 5.

With the can guiding arm 146 resting on top of the can the spring 142 is in a state of compression and causes the arm 146 to press tightly against the top of the can 48. In this manner the can guiding arm 146 cooperates with the driving wheel 40 and its shoulder member 72 to maintain the can 48 in a cutting position relative to the rotary cutter 78. Also, when the can guiding arm 146 is resting on the top of the can 48 the arm member 128 is positioned to cause the switch arm 126 to engage the other contact 122, thereby again completing the electrical circuit to the motor 24.

At vertical positions for the can guiding arm 146 between its normal position, as illustrated in FIGURES 1 and 4, and its raised position illustrated in FIGURE 5, the switch 120 is open. Thus, when, by operation of the rotary cutter 78 and the driving wheel 49, the top has been severed from the can 48, the spring 142 forces the can guiding arm 146 and arm member 128 downward to open switch 120 which interrupts the electrical circuit including motor 24. In this manner the motor 24 is automatically shut off when the top has been completely severed from the can 48.

As previously mentioned, the housing 10 of the present invention includes a cover section 28 (see FIG. 2). The cover section is mounted over a portion of the rear section 16 of the housing 10 to provide a cover for the knife sharpener apparatus 151 of the present invention. The knife sharpener apparatus 151 includes a grinding wheel 148 mounted for rotation with and, in part, around the motor shaft 26, as hereinafter explained. To guide a knife or other blade into contact with the sides 159 and 152 of the grinding wheel 148 the cover section 28 has a pair of slots 154 and 156 formed in its upper surface. The slots 154 and 156 extend down and inward at an angle toward the sides of the grinding wheel 148 to define side walls 158, 160, 162 and 164 which guide a knife blade into contact with the sides 158 and 152, respectively, of the grinding wheel 148. In this manner, a knife blade in contacting the grinding wheel exerts a force thereon having vertical and horizontal components which urge the gringing wheel 148 axially along the motor shaft 26.

To resist the axial movement of the grinding wheel 148 as well as to couple the wheel to the shaft 26 for rotation therewith, the apparatus of the present invention includes a coupling arrangement 166 between the shaft 26 and the grinding wheel 148 which possesses a preselected torque transfer characteristic. This means that Whenever an external force is applied to the grinding wheel 148 which requires a greater transfer of torque than the one pre-selected, slippage will occur between the shaft 26 and the grinding wheel 148. A preferred embodiment of such a coupling arrangement is illustrated in FIG- URE 6.

As represented, the coupling arrangement 166 generally includes a bearing shaft 168, wheel bushings 196 and 198 supported thereon and means to frictionally couple the shaft to the bushings. More specifically, the coupling arrangement includes a shaft extension or bearing shaft 168 having an outwardly flanged end section or hub 170 that defines an annular shoulder 172 which extends around the shaft 168. The shaft 168 also includes a threaded bore 174 to receive the reduced diameter, threaded extension 176 of the shaft 26. Positioned on reduced end of the shaft 168 are washer members 178 and 180. Preferably, the washer 178 is composed of a hard metal, such as steel, while the washer 184) is composed of a relatively soft fibrous material. On the other side of the grinding wheel 148, washers 182 and 184 encircle shaft extension 168 intermediate shoulder 172 and bushing 196. Preferably, the washer 184 is composed of a hard metal, such as steel, while the washer 182 is composed of a relatively soft fibrous material.

The grinding wheel 148 is apertured at 186 with a central reduced radii section defining annular shoulders 192 and 194 adjacent counterbores 188 and 190.

Bushings 196 and 198 are apertured to receive the shaft 168 and also mount the grinding wheel 148. The bushings 196 and 198 include outwardly flanged end sections for engaging the respective shoulders 192 and 194 of the grinding wheel 148. Preferably, the bushings 196 and 198 are composed of a relatively soft metal or a plastic-like material such as zinc, brass, nylon, Teflon, etc. In this manner a bushing of relatively soft material is maintained in contact with the shaft extension 168.

Coupling between the grinding wheel 148 and the shaft 168 is obtained by biasing the spring washer 208 which is located between the washer 184 and the bushing 196. As illustrated, the spring washer 208 is positioned with its concave surface outwardly and, when loaded, exerts a resilient force on the bushing 196 which urge the grinding wheel 148 toward the shoulder on the end of the shaft 26. The spring washer 200, and the bushings 196 and 198 are constructed to make a controlled friction contact with the surface of the shaft 168. Under normal operating conditions, the force provided by the spring 288 to urge the bushing 198 against the fiber Washer 188 and the friction contact between the bushings 196 and 198 and the shaft 168 are sufficient to lock the grinding wheel 148 to the shaft 168. However, these elements define a spring-loaded slip clutch which possesses a predetermined torque transfer characteristic, depending on the degree to which shaft 26 is threadedly telescoped into the shaft extension 168. Thus, as defined above, when a force is exerted on the grinding wheel M8 which requires a transfer of torque greater than the preselected characteristic of the clutch, the clutch slips. In the coupling arrangement 166 of the present invention the clutch is constructed to compensate for the drag on the grinding wheel by the pressure of a knife blade up to the point when the maximum torque transfer characteristic is reached which uncouples the grinding wheel 148 and the shaft 168.

For example, when a knife blade is guided into pres sure contact with the right hand side 1553 of the grinding wheel 148, the grinding wheel tends to move axially along the shaft 168 toward the end of the motor shaft 26. This compresses the fiber washer 188 and urges the metal washer 1'78 against the motor shaft 26 which increases the torque that the clutch is required to transfer from the grinding wheel 148 to the shaft 168. However, when the pressure of the blade reaches the predetermined safe maximum, the torque transfer characteristic of the clutch is exceeded and the clutch permits the shaft 168 and the motor shaft 26 to rotate relative to the bushings 196, 198 and the grinding wheel 14-8.

In a similar manner, when the blade is guided into pressure contact with the left side 152 of the grinding wheel 148, the grinding Wheel 148 tends to move axially toward the shoulder 172. This compresses the spring washer 209 and increases the coefiicient of friction between washers 182, 184 and shoulder 172 to compensate for the added drag on the grinding wheel 148. However, when the pressure of the blade reaches the predetermined safe maximum the torque transfer characteristic of the clutch is again exceeded to cause the clutch to slip. This again allows the shaft 168 to rotate relative to the grinding Wheel 1 38 to thereby protect the blade from possible damage.

Thus, the present invention includes a knife sharpening arrangement having a grinding wheel 148 which is coupled by a single slipping clutch arrangement 166 for rotation with the motor shaft 26 to sharpen knives and which is effectively disengaged from the motor shaft when a predetermined maximum safe pressure is exerted on the wheel by a blade.

As illustrated in FIGURE 2, a fan 282 is fixably supported on the shaft 26 between the motor 24 and the grinding Wheel 1 18 of the knife sharpener 151. As the shaft 26 rotates in response to the operation of the motor 24, the fan blows air past the motor 24, thereby effecting a cooling of the motor.

A preferred arrangement for the fan is illustrated in FIGURE 8. As represented, the fan is coupled to the shaft 26 at a side of the motor 24 remote from the grinding wheel 148. Pressure fitted between the cover section 28 and a lower surface of the housing 10 is a dust shield 204. The dust shield 284 includes an opening 286 permitting the shaft 26 to pass therethrough. The dust shield 2116 together with the housing It), forms a compartment 288 for the motor 24 which is isolated from the grinding Wheel 148. Thus, the fan 2412 cools the motor 24 with out allowing shavings, dust and the like, from the area around the grinding wheel 148 from entering into contact with the motor 24.

spaced apart shoulders mounted within the housing;

electric circuit means for energizing the motor;

a grinding wheel having an interior, Teflon-type split bushing rotatably supported on the shaft intermediate said shoulders;

means including the housing for supporting and guiding a blade to be sharpened into engagement with a side of the Wheel such that the blade, in being pressed against the Wheel, exerts a force on the wheel tending to slide the wheel axially on the shaft;

compressible fiber washers disposed intermediate said shoulders and said bushing;

and a spring-biased slip clutch connected between the shoulder on one side of the wheel and one side of said wheel bushing to urge said bushing against the other shoulder, said clutch having a predetermined torque transfer characteristic which allows the bushiing and Wheel to slip relative to the shaft before the axial force of the blade against the wheel is sufficient to damage the blade.

2. An electric sharpener for knives in accordance with claim 1 wherein said wheel is counterbored on one side, the spring of said slip clutch is convex shaped and the convex face thereof abuts a side of said bushing interior of said counterbore and means are provided to seal said spring interior of said counterbore.

3. An electric sharpener for knives and the like comprising, in combination,

a housing;

an electric motor having a shaft mounted within the housing, said shaft having a reduced section at its outer end;

a shaft extension telescoping over the reduced section of said motor shaft, said shaft extension having a hub at its outer end which defines a shoulder;

a centrally apertured grinding wheel having counterbores on each side thereof;

a two-part, Teflon-type bushing affixed interior of the aperture of the grinding wheel to mount the grinding wheel on said shaft extension intermediate the shoulders on said motor shaft and said shaft extension; and

an apertured, cup-shaped spring member mounted on said shaft extension interior of one of said counterbores with its convex side bearing against one side of said bushing;

a first washer mounted on said shaft extension intermediate said resilient member and one of the said shoulders and proportioned to seal the spring member interior of said counterbore;

a second washer mounted on said shaft extension intermediate the other of said shoulders and the other side of said bushing and the small end of said shaft extension;

fiber washers mounted on said shaft extension between the shoulder thereof and said first washer and between said second washer and the end of said bushing and said shaft extension;

and means to compress said spring member axially to provide a preselected torque transfer characteristic for the grinding Wheel whereby said shaft extension and said bushing means rotate as a unit until the torque transfer characteristic is exceeded, at which point slippage therebetween occurs.

References Cited in the file of this patent UNITED STATES PATENTS 2,775,075 McMaster et al. Dec. 25, 1956 2,799,125 Dicke July 16, 1957 2,860,452 Lebus Nov. 18, 1958 2,897,637 Bodle Aug. 4, 1959 2,898,709 Bednarski Aug. 11, 1959 3,071,899 Hicks Jan. 8, 1963 FOREIGN PATENTS 663,598 Great Britain Dec. 27, 1951 1,091,563 France Oct. 27, 1954 

1. AN ELECTRIC SHARPENER FOR KNIVES AND THE LIKE COMPRISING: A HOUSING; AN ELECTRIC MOTOR HAVING A SHAFT WITH SPACED APART SHOULDERS MOUNTED WITHIN THE HOUSING; ELECTRIC CIRCUIT MEANS FOR ENERGIZING THE MOTOR; A GRINDING WHEEL HAVING AN INTERIOR, TEFLON-TYPE SPLIT BUSHING ROTATABLY SUPPORTED ON THE SHAFT INTERMEDIATE SAID SHOULDERS; MEANS INCLUDING THE HOUSING FOR SUPPORTING AND GUIDING A BLADE TO BE SHARPENED INTO ENGAGEMENT WITH A SIDE OF THE WHEEL SUCH THAT THE BLADE, IN BEING PRESSED AGAINST THE WHEEL, EXERTS A FORCE ON THE WHEEL TENDING TO SLIDE THE WHEEL AXIALLY ON THE SHAFT; COMPRESSIBLE FIBER WASHERS DISPOSED INTERMEDIATE SAID SHOULDERS AND SAID BUSHING; AND A SPRING-BIASED SLIP CLUTCH CONNECTED BETWEEN THE SHOULDER ON ONE SIDE OF THE WHEEL AND ONE SIDE OF SAID WHEEL BUSHING TO URGE SAID BUSHING AGAINST THE OTHER SHOULDER, SAID CLUTCH HAVING A PREDETERMINED TORQUE TRANSFER CHARACTERISTIC WHICH ALLOWS THE BUSHING AND WHEEL TO SLIP RELATIVE TO THE SHAFT BEFORE THE AXIAL FORCE OF THE BLADE AGAINST THE WHEEL IS SUFFICIENT TO DAMAGE THE BLADE. 